Processes exist for automatically detecting so-called “letterbox” formats comprising black horizontal bars at the top and bottom of the television image. These processes are generally based on a measurement of the video levels over the first few and last few lines of the video image. It is as a function of the luminance levels averaged over these first few lines and over these last few lines that the “letterbox” format is detected.
These processes are however not very reliable since they depend on luminance settings, on the signal/noise ratio, on the insertion of logos into the black bands, etc.
The purpose of the invention is to alleviate the aforesaid drawbacks.